Balasubramaniyan Rajagopalan

Highly-ordered maghemite/reduced graphene oxide nanocomposites for high-performance photoelectrochemical water splitting

Highly ordered γ-Fe2O3/reduced graphene oxide (RGO) was synthesized via a facile solution technique combined with calcination at various temperatures. The maghemite iron oxide structure was obtained on the GO surface and improved crystallinity of γ-Fe2O3 was observed as the calcination temperature increased. The prepared highly ordered maghemite structure on RGO exhibited an excellent water splitting performance under UV light (∼360 nm) illumination. The photocurrent density of RGO/γ-Fe2O3 calcined at 500 °C was 6.74 mA cm−2 vs. RHE and a high incident photon to current conversion efficiency (IPCE) of 4.7%, was achieved. This photocurrent density and the IPCE values are 3.7 times and 4 times higher than that of pristine iron oxide, respectively.

Comparative supercapacitance performance of CuO nanostructures for energy storage device applications

In the present study, three different morphologies of copper oxide (CuO) nanostructures; bud-, flower- and plate-shaped CuO structures were synthesized by a simple chemical method. Binder-included pseudocapacitor electrodes were prepared using bud- and flower-shaped CuO structures whereas, directly grown CuO-nanoplates on Ni foam were used as a binder-free electrode in a three-electrode setup for electrochemical studies. Remarkably, the binder-free CuO nanoplates electrode exhibited excellent specific capacitance of 536 F g−1 at a current density of 2 A g−1, whereas the binder-included electrodes of bud- and flower-shaped CuO exhibited 230 F g−1 and 296 F g−1, respectively, at a current density of 0.7 A g−1 in a 6 M KOH electrolyte. The cycling retention test and charge/discharge stability for the binder-free CuO nanoplates electrode showed 94% capacity retention after 2000 cycles and capacitance loss of only 11.3% over ∼1000 cycles at a current density of 4 A g−1 from charge/discharge measurements. Also, the binder-free CuO electrode showed higher energy and power densities of 29.4 W h kg−1 and 12.7 W kg−1, respectively, at 1.96 A g−1 in an asymmetrical device, when compared to the binder-included electrode of flower-shaped CuO.

High performance bifunctional electrocatalytic activity of a reduced graphene oxide–molybdenum oxide hybrid catalyst

The advances in cost effective, highly active and stable electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) remain the major issues for the commercialization of metal air-batteries and alkaline fuel cells. In this aspect, a facile hydrothermal route was developed to prepare nonprecious metal electrocatalysts including pristine MoO3 rods, nanospheres, and their hybrids with reduced graphene oxide (rGO). This is the first report of the use of rGO coupled with hexagonal MoO3 nanocrystals that act as both ORR and OER catalysts. The rGO–MoO3 sphere hybrid catalyst exhibited excellent catalytic activity toward both the ORR and OER compared to pristine MoO3 rods, MoO3 spheres and rGO–MoO3 rods. In addition, the rGO–MoO3 nanosphere hybrid exhibited excellent catalytic activity, long-term durability, and CO tolerance compared to a high quality commercial Pt/C catalyst. This makes the GMS hybrid composite a highly promising candidate for high-performance non-precious metal-based bi-functional electrocatalysts with low cost and high efficiency for electrochemical energy conversion. The enhanced activity of the rGO–MoO3 nanosphere hybrid is due mainly to the enhanced structural openness in the tunnel structure of the hexagonal MoO3 when it is coupled with rGO.

A double core–shell modification of bulk TiO2 microspheres into porous N-doped-graphene carbon nanoflakes/N-doped TiO2 microspheres for lithium-ion battery anodes

In this study, we modified bulk TiO2 microspheres—using a template-aided, double core–shell modification with N-doped carbon (NC) and N-doped graphene (NG)—for the purpose of forming porous N-doped graphene carbon nanoflakes/N-doped TiO2 (NG–NC/NTiO2) microspheres. The effects of surface modification on the properties of the TiO2 microspheres and the resultant electrochemical performance in a lithium-ion-battery (LIB) anode were thoroughly investigated. The double core–shell modified nanocomposite exhibited a specific capacity of 74 mA h g−1 at a 10 C rate, which was much higher than the capacities of TiO2, carbon/TiO2, and core–shell NC/NTiO2 nanocomposites at rates of 0.2, 1, and 5 C, respectively. The RGO of the double core–shell NC/NTiO2 nanocomposite provided an effective buffering effect for the TiO2 microsphere, resulting in a much lower initial specific-capacity loss of 19.6%, on the 200th cycle, in comparison with the 41.8% loss of the core–shell NC/NTiO2 nanocomposite at the same cyclic stage. Such excellent performances from the TiO2 microspheres with the double core–shell assembly in the LIB anode were attributed to a significant reduction of charge transfer resistance (Rct) and maintenance of electrode stability.